Special permanent magnets, i.e., which are matched to the stringent requirements of electrical machines, have been successfully developed. Such magnets are used to produce the rotating magnetic field in the rotating electrical machines. Various options for the arrangement of the permanent magnets in the rotor or in the stator have been developed for motors and generators with rated powers up to 30 kW at 3000 rpm. In this case, “flux concentration construction” has been found to be the technically better solution above a rated power of several hundred watts. One embodiment of this construction is to arrange the permanent magnets in the pole gaps in the rotor (Siemens Journal 49, 1975, Issue 6, page 368 et seq./369, FIG. 3). One known design solution for this purpose is to arrange the permanent magnets, which have a flat rectangular cross section and are designed to be flat in the magnetization direction, radially with respect to the rotor axis in slot-like spaces in each case between two yokes that are fixed on the rotor body (EP 0 582 721 B1).
Rotors, fitted with permanent magnets for an electrical machine, and having poles which are welded to a hollow rotor shaft are shaped in such a manner that there is an accommodation area with a trapezoidal cross section between two poles, for permanent magnets which likewise have a trapezoidal cross section. The outer surface of the rotor is, in this case, formed by shrunk-on reinforcements composed of a copper-beryllium alloy (U.S. Pat. No. 4,242,610).
To handle of permanent magnets when constructing rotors of electrical machines, the magnet bodies are installed in the unmagnetized state and are magnetized once they have been arranged on the rotor, for example using the stator winding of the electrical machine (EP 0 195 741 B1).
Magnets which store a large amount of energy, for example based on neodymium-iron-boron (NeFeB), have been developed recently. The use of permanent-magnet rotors is now feasible even for electrical machines with a rated power of more than 100 kW, for example in ship propulsion systems with a rated power of 5 to 30 W. Machines such as these have a rotor diameter of more than 25 cm up to about 300 cm. If the rotors of machines such as these are constructed using flux concentration, this involves difficulties in the installation and securing of the magnets.